In the operation of robotic systems particularly manipulators having articulated joints it is generally the practice to use joint angle sensors such as encoders or resolvers to determine the relative angular displacement between a pair of pivotably interconnected arms.
Obviously such joint angle sensors are subject to failure as is in the other detecting system including the one which is described here below. However, as man becomes more and more dependent on the operation of these sensors to handle relatively large machinery, a backup system to ensure the accurate operation of the sensor or an alternate system for determining the relative angular relationship between a pair of interconnected joints is of value.